1. Field of the Invention
The present invention relates to a method of, and apparatus for, quantitatively detecting the optical axis of a headlamp of a vehicle such as automobile under inspection.
2. Prior-art Statement
For detecting the main optical axis of a headlamp of a car, for example, after assembled, it has been proposed to use a screen having illuminance sensors provided thereon and onto which a light is projected from the headlamp.
Recently, a wider variety of cars has adopt halogen lamps. In these circumstances, it has been proposed to detect the headlamp optical axis of a headlamp by picking up, by a TV camera or the like, a luminous intensity distribution pattern of a light projected onto such a screen, processing the light image, enclosing, by a line, an area of an illuminance having a greater value than a predetermined one to define an equiluminous contour, for example, and calculating a position of the center of gravity (centroid or center of figure) of the equiluminous contour and taking it as the main optical axis of the headlamp.
When such conventional method is used to detect a main optical axis, however, the equiluminous contour will vary greatly depending upon the setting of an illuminance which is a reference for definition of the equiluminous contour so that a plurality of so-called hot zones is likely to be set, resulting in a possibility that an optical axis position to be set will deviate greatly from its due position, as shown in FIG. 9. That is, as shown in FIG. 9, when an equiluminous contour is defined with reference to the illuminance S.sub.1, for example, the center of gravity G.sub.1 coincides nearly precisely with the optical axis position. However, if an equiluminous contour is defined with reference to the illuminance S.sub.2, for example, two hot zones will be set. Also, if an equiluminous contour is defined with reference to the illuminance S.sub.3, the center of gravity G.sub.3 will greatly deviate from the optical axis position. In these cases, the position of the center of gravity may not be regarded as the optical axis position, so it is difficult to detect the headlamp optical axis with a high accuracy.